BQ24295 Datasheet, PDF (31/45 Pages) Texas Instruments – I2C Controlled 3A Single Cell USB Charger

bq24295
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SLUSBC1 – SEPTEMBER 2013
Host Mode and Default Mode
The device is a host controlled device, but it can operate in default mode without host management. In default
mode, the device can be used as an autonomous charger with no host or with host in sleep.
When the charger is in default mode, REG09[7] is HIGH. When the charger is in host mode, REG09[7] is LOW.
After power-on-reset, the device starts in watchdog timer expiration state, or default mode. All the registers are in
the default settings. The device keeps charging the battery by default with 12-hour fast charging safety timer. At
the end of the 12 hours, the charging is stopped and the buck converter continues to operate to supply system
load.
Any write command to device transitions the device from default mode to host mode. All the device parameters
can be programmed by the host. To keep the device in host mode, the host has to reset the watchdog timer by
writing 1 to REG01[6] before the watchdog timer expires (REG05[5:4]), or disable watchdog timer by setting
REG05[5:4]=00.
When the host changes watchdog timer configuration (REG05[5:4]), it is recommended to first disable watchdog
by writing 00 to REG05[5:4] and then change the watchdog to new timer values. This ensures the watchdog
timer is restarted after new value is written.
POR
watchdog timer expired
Reset registers
I2C interface enabled
Y
I2C Write?
N
Default Mode
Reset watchdog timer
Reset registers
Host Mode
Start watchdog timer
Host programs registers
Reset REG01
Y
bit[6]?
N
Y
N
I2C Write?
Y
Watchdog Timer
N
Expired?
Figure 31. Watchdog Timer Flow Chart
Status Outputs (STAT, and INT)
Charging Status Indicator (STAT)
The device indicates charging state on the open drain STAT pin. The STAT pin can drive LED as the application
diagram shows.
Table 6. STAT Pin State
CHARGING STATE
Charging in progress (including recharge)
Charging complete
Sleep mode, charge disable
STAT
LOW
HIGH
HIGH
Interrupt to Host (INT)
In some applications, the host does not always monitor the charger operation. The INT notifies the system on the
device operation. The following events will generate 256us INT pulse.
1. USB/adapter source identified (through DPDM detection)
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